With the development of science and technology, wearable electronic devices already have a function of heartbeat detection. However, the heartbeat signal detected by the heartbeat detection circuit in the wearable electronic device is very weak. To amplify the heartbeat signal to a quantifiable level, it is necessary to amplify the heartbeat signal detected by the heartbeat detection circuit by a programmable gain amplifier.
Specifically, the programmable gain amplifier is coupled to a pre-stage circuit such as a heartbeat detection circuit and a post-stage circuit such as an analog-to-digital converter (ADC). In general, the common-mode voltage of the output signal of the pre-stage circuit does not match the common-mode voltage of the programmable gain amplifier. When the post-stage circuit of the programmable gain amplifier does not match the common-mode voltage of the programmable gain amplifier itself, this may cause some problems such as an offset voltage of the post-stage circuit is changed, and the input common-mode point may be shifted, furthermore, the post-stage circuit cannot work normally when the condition is very serious. In addition, in the conventional switched capacitor common-mode negative feedback circuit, the programmable gain amplifier has to take a lot of time to establish a common-mode negative feedback of the programmable gain amplifier, such that the average power consumption of the programmable gain amplifier is increased.
In addition, the output signal of the heartbeat detection circuit includes a heartbeat signal and a baseline signal, the amplitude of the heartbeat signal is only 1/100˜ 1/1000 of that of the baseline signal, and in a Deep Submicron integrated circuit, the dynamic range of the programmable gain amplifier is only about 1V, such that the programmable gain amplifier comes into saturation due to the baseline signal when the heartbeat signal has not been amplified to a desired magnitude.
Therefore, there is a need for improvement in the related art.